Chain tensioner upgrade Q

cowtown · 09-29-2002, 11:25 AM

Hi guys,
I'm slowly going through a 1977 930 (3.0 Turbo Carrera) engine and am planning on upgrading to pressure-fed tensioners while I'm in there. I have the tensioner upgrade kit (Automotion brand) and am confused by one of the instructions:

"On any of the 1967-1979 engines, if the old style chain wheel supports are used, then spacers (930.105.513.00) are needed between the wheel supports and the new tensioners. If the engine has been updated to the late-style, mid-1980 and later chain wheel supports, which we strongly recommend, then these spacers are not necessary."

I find no mention of this wheel support update in BA's book or my shop manuals. Can someone fill me in? What's the purpose of the newer chain wheel supports, and do I need to go this route or would the spacers be OK?

Finally, how do I verify that I do indeed have the old wheel supports? There's no part number on the support, but the chain wheel it is attached to reads 901.105.545.03.

Thanks a lot for any help with this!
Colin

Early_S_Man · 09-29-2002, 12:18 PM

Colin,

There is actually a picture and information about the changes on pages 78 and 83 of BA's second edition.

There can be no mistaking the parts ... if you examine the bore/bearings of the idlers you have. Mid production like your engine originally came with ... had a plain bore and no bushing. Later updated idlers had two distinct bushings and the 'turbo' tensioners used with them had the same thickness mounting tab as the pressure-fed tensioners, thinner than on the early tensioners!

cowtown · 09-29-2002, 04:08 PM

Warren,
Thanks very much! I've been reading and re-reading the "rebuilding" section when it was right there in the previous chapter!

I definitely have the non-bushed early style shown in the middle...I'll upgrade to the later ones.

Thanks,
Colin

Wayne 962 · Wayne 962's Garage

These are in our catalog, and are significantly less than Automotion's price as well. You probably could have saved about $100 if you bought the tensioner kit from us too:

http://www.pelicanparts.com/catalog/shopcart/911M/por_911M_enginC_main.htm

Also, the answers to your questions are also in 101 Projects...

-Wayne

Jocke · Jocke's Garage

Put the 4:th cylinders piston in their top-position and make sure that the rotor stands against the same four in the distrubution box.

In that way the chain would be in the loosest position.

It´s makes the change a lot easyer.

Good luck.

/Jocke

cowtown · 09-30-2002, 08:26 AM

[QUOTE]Originally posted by Wayne at Pelican Parts
[B]These are in our catalog, and are significantly less than Automotion's price as well. You probably could have saved about $100 if you bought the tensioner kit from us too:

Wayne, the tensioners were in the box of "Porsche Junk" (so said the label) that came with the engine...I OF COURSE would have bought them from you, and will never mention Automotion on this board again

I also do have your book, but my no-good 911-owning neighbor ran off with it before I could read it.

Jocke: Thanks for the added advice!

Superman · 09-30-2002, 10:48 AM

Automotion makes a nice catalogue, which is convenient when I want to see pictures of the things I'm ordering from Pelican. I'd be surprized if I found ANYTHING at Automotion that Wayne did not offer at lower cost. And nobody beats Pelican for product support. It's a no-brainer. Once the box marked Porsche Junk is empty.

And the later chain wheel supports are STRONGLY recommended.

Wayne 962 · Wayne 962's Garage

It's not difficult to beat Automotion's price - those catalogs are expensive.

"Put the 4:th cylinders piston in their top-position and make sure that the rotor stands against the same four in the distrubution box.

In that way the chain would be in the loosest position. "

What on earth is this? The chain should NOT BE LOOSE AT ANY TIME!!! This is just plain bad advice, and can cause someone to completely wreck their engine. We've already had two people here who bent valves because they let tension in the chain go slack...

-Wayne

05-02-2003, 08:00 AM

Cowtown, I also have a 1977 930 turbo. I'm planning the tensioner upgrade. Would you please advise me the correct part numbers for the chain wheel supports you used when you did your upgrade? I looked in the parts search, but just want to sure I'm double sure I'm ordering the right parts. Thanks.

cowtown · 05-02-2003, 08:13 AM

Hi Evergreen, The parts I used were:
Left: 93010550900
Right: 93010551000

These do NOT require the additional spacer and have worked fine for me.
Good luck!
Colin

05-02-2003, 08:27 AM

Cowtown, THANK YOU!!! Appreciate the part #'s. I have the "special" tool keep the tension on the chains. Hope it works. I also bought the Automotion brand of tensioner upgrade, before I knew of Pelican Parts. Did you encounter any difficulty in swapping out the wheel supports? After I get the tensioner ugrade done, I'm installing a 79' intercooler, and k27, and the later style exhaust, with the cat removed. It should really scream then!

cowtown · 05-02-2003, 08:39 AM

No problems with the Automotion upgrade so far, though it sat in a box for many, many years, so I'm not sure if it will begin leaking prematurely.

Do you already have the intercooler parts? Where did you get them, and do you have pictures? I will consider doing this when I get my car running well. I've got a later Turbo tail in anticipation of this.

PS I PMed you with more informtion about the chain wheels.

HarryD · 05-02-2003, 08:39 AM

Hello,

I discussed this upgrade with my local p-car expert and asked him about the chain wheel.

For better or worse, he told me that the failure mode for the tensioners is a complex interplay between the less than optimum damping of the non-pressure fed tensioners, geometry of the pre-upgraded chain wheel and the ability of later Porsche engines to provide sufficient (read drivable) torque in the 2,000 - 2,500 rpm range. At this low rpm range, there is a harmonic that causes the chain to vibrate rapidly and wear out the tensioner. The pressure fed tensioner damps this motion more effectively. Add the improvement to the chain geometry due to the chain wheel change, and voila! tensioner failure are much less frequent.

Do I have my facts straight?

cowtown · 05-02-2003, 08:48 AM

Harry, I think all of what you said is probably true. I don't consider myself smart enough to understand the physics of everything that's going on in there. But I'm smart enough to do a bunch of research

The biggest issue with the old-vs-new style is that there is a BUSHING on the later style to keep the support from binding.

I tend to try to do what those who have been successful recommend (ie Bruce Anderson, and some of the brighter people on this board). Since it was only $100, I think it's a must-do upgrade.

05-02-2003, 08:50 AM

Cowtown, same issue with my tensioners. They have been sitting for a couple of years also! As far as the intercooler is concerned, I really lucked out on Ebay last week. I picked up the intercooler, BOV manifold, K27, air cleaner assembly, and later style exhaust/cat for $600.00! I think the seller was in a hurry to get rid of these parts, since I made an offer to him over the phone that he accepted before the auction closed. I'll keep you posted as work progresses.

HarryD · 05-02-2003, 11:32 AM

Quote:

Originally posted by cowtown
Harry, I think all of what you said is probably true. I don't consider myself smart enough to understand the physics of everything that's going on in there. But I'm smart enough to do a bunch of research The biggest issue with the old-vs-new style is that there is a BUSHING on the later style to keep the support from binding.

I tend to try to do what those who have been successful recommend (ie Bruce Anderson, and some of the brighter people on this board). Since it was only $100, I think it's a must-do upgrade.

Agreed!

I just think we should understnad the whys behind what we are doing. If anything, this should be an incentive for those who haven't yet to upgrade.